How about a standard switch and extend the switch bit, so the knife bit isnt live just use to throw the real switch. A standard light switch extended by say 6 inches would give a good long "throw" without any danger.

Use a low voltage on the knife switch, say 12v, and use it to trigger a relay or contactor You can have it as exposed as you like and not present any real risk. Contactors engage with a nice "clunk". If you can't get one with a 12v coil, trigger it from a small relay. That said, even a small sugar-cube relay will switch 5-10 amps.

Ah yes,I probably should have put that in my original post.......The switch would be build from scratch,involving very low voltages(most likely battery powered,9 V ,or a 12 V adapter),using one wire.And used in an automaton and/or lamp.This is what I'm after:

The 'original' was, quite literally, a knife - not double-poled, but single: a knife with a blunted tip, drilled to act as a hinge, with 'clips' to receive the portion of the conductive blade near the haft/guard/pommel (depending on type of knife).

..and the twin bladed one is just two knives joined across the top (or formed out of a U shaped piece of material). The two blades just double the contact area. From memory (a long while ago) the power or common wire was taken to the centre pair of posts (knife pivots) and the the output from one pair of outer contacts. Each pair of contacts are paralleled. This also allowed you to switch to two different circuits. These kind of switches were used for low current devices, like voltmeters, ie connect a VM to the pivots and two measured circuits. The contacts that the knife blade slid into are quite critical as they need to have a good area of contact and needs to be sprung to provide a good grip on the blade. Have a good look at some originals.

Correct - when dealing with voltage, you are dealing with resistance - and resistance, to simplify, can be considered as a funtion of available mass. (Thus, 12-gauge wire handles more current than a 14-gauge wire, with the same 'resistance factor'; or, alternately: 12g offers more 'leeway' than 14g... assuming 14g is spec'd to handle said (assumed) load in the first place... *Grin*)

Alas, however, I fear we are wandering a touch O/T - judging from the OP, we are well and truly below a point where any such consideration would possibly become 'non-trivial'.

There is a variation (sorry, no pics) that provided a "quick break" disconnection. The blades were as shown, but the section of the blade that made the contact, was hinged and held close to the remainder of the blade by a spring. When the lever was pulled to disconnect the power, the sprunk part of the blade remained in contact, held by the contact side pressure, until it reached the point where the tension in the spring overcame the resistance in the contacts and the 'knifelets' shot out of the contacts with a most satisfying noise (and smoke and sparks if you were really lucky careless.)

How about a standard switch and extend the switch bit, so the knife bit isnt live just use to throw the real switch. A standard light switch extended by say 6 inches would give a good long "throw" without any danger.

Part of the appeal of the knife switches in the horror movies is the shower of sparks given off when the knives touch the contacts. Is there a way that this can be achieved without putting the user at risk of electrocution?

Part of the appeal of the knife switches in the horror movies is the shower of sparks given off when the knives touch the contacts. Is there a way that this can be achieved without putting the user at risk of electrocution?

This is what I thought, too. While it is a good, safe idea to have a low voltage circuit energise a relay to switch the high voltage, you're not going to get the dramatic spark.

But as I understand it, the spark is caused by high voltage, while the danger comes from high current.

So to combine dramatic sparks from high voltage with safety from low current, my idea would be a circuit to transform 240V (or 110V for you colonials) on a 5A circuit to supply the blade switch with something stupidly dramatic like 1000V at 100mA that then energises the relay.

MODERATOR NOTE: 1000V @ 100 mA = 100 W, which is quite enough to make you permanently dead. DO NOT ATTEMPT THIS!

Part of the appeal of the knife switches in the horror movies is the shower of sparks given off when the knives touch the contacts. Is there a way that this can be achieved without putting the user at risk of electrocution?

This is what I thought, too. While it is a good, safe idea to have a low voltage circuit energise a relay to switch the high voltage, you're not going to get the dramatic spark.

But as I understand it, the spark is caused by high voltage, while the danger comes from high current.

So to combine dramatic sparks from high voltage with safety from low current, my idea would be a circuit to transform 240V (or 110V for you colonials) on a 5A circuit to supply the blade switch with something stupidly dramatic like 1000V at 100mA that then energises the relay.

I understand that when they film Dramatic Sword Fights for the cinema, they electrify the swords somehow to make them draw sparks when they clash. They generally have very expensive actors beating on each other with those selfsame swords, so they can't be that dangerous; perhaps something like that would serve your purpose if you could figure out the specs?

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I just remembered that one of my childhood books on electricity described how to make sparks with a battery, some wires, and a nail file; I tried it back ten, and it worked. Wire file to one battery terminal; brush wire lead from other terminal across the rough side of the file. Small sparks fly from where the wire contacts the file.

This method could possibly be employed to produce a spark effect for mock-up props.